Methods and apparatus for dual connectivity operation in a wireless communication network

ABSTRACT

Dual-connectivity for the User Equipment (UE) in a cellular network is performed by monitoring a plurality of cells. During dual-connectivity, the UE may be simultaneously connected to one serving cell for the Control Plane (C-plane) and to another serving cell, controlled by a different eNodeB, for the User Plane (U-plane). In another embodiment, the dual-connected UE monitors a Physical Downlink Control Channel (PDCCH) from the first eNB and monitors an EPDCCH from the second eNB.

CLAIM TO PRIORITY UNDER 35 U.S.C. 119

The present application claims priority to and incorporates by referenceU.S. provisional application No. 61/750,904 filed on Jan. 10, 2013,entitled “Physical layer signaling mechanisms for Dual-Connectivity inLTE-Advanced.”

FIELD OF THE INVENTION

This invention generally relates to wireless cellular communication, andin particular to User Equipment simultaneously connected to at least twoserving cells controlled by different base stations.

BACKGROUND OF THE INVENTION

Wireless cellular communication networks incorporate a number ofwireless terminal devices and a number of base stations for the purposeof providing communications services such as telephony, data, video,messaging, chat and broadcast. A number of wireless terminals can beconnected to a serving cell that is controlled by a base station (BS).Typical access schemes employed in widely used cellular networks includeFrequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Code Division Multiple Access (CDMA), Orthogonal FrequencyDivision Multiple Access (OFDMA), Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) or combinations thereof. The base station (BS)may also be called a NodeB in the Universal Mobile TelecommunicationsSystem (UMTS) specified by the Third Generation Partnership Project(3GPP), a base transceiver system (BTS), an access point (AP), or someother equivalent terminology. As improvements of networks are made, theNodeB functionality evolves, so a NodeB is also referred to as anevolved NodeB (eNodeB or eNB) in the 3GPP Long Term Evolution (LTE)system. In general, eNodeB hardware, when deployed, is fixed andstationary.

In contrast to the eNodeB, the wireless terminal devices can be portablehardware. The wireless terminal device is commonly referred to as a UserEquipment (UE), a mobile station, a cellular phone, a personal digitalassistant (PDA), a wireless modem card, and so on. Uplink (UL)communication refers to communication from a fixed or mobile UE to theeNodeB, whereas downlink (DL) communication refers to communication fromthe eNodeB to the fixed or mobile UE. Each eNodeB contains radiofrequency transmitter(s) and receiver(s) used to communicate directlywith the mobiles, which move either freely around it or are also at afixed location. Similarly, each UE contains radio frequencytransmitter(s) and receiver(s) used to communicate directly with theeNodeB.

Long Term Evolution (LTE) wireless networks, also known as EvolvedUniversal Terrestrial Radio Access Networks (E-UTRAN), are beingstandardized by the 3GPP working groups (WGs). OFDMA and SC-FDMA accessschemes are employed for the downlink (DL) and uplink (UL) of E-UTRAN,respectively as part of the Evolved Universal Terrestrial Radio Access(E-UTRA). User Equipments (UEs) are time, frequency or code multiplexedon a physical uplink shared channel (PUSCH) for transmitting UplinkShared Channel (UL-SCH) data, and a fine time and frequencysynchronization between UEs guarantees optimal intra-cell orthogonality.In case the UE is not UL synchronized, it may initiate the random accessprocedure for synchronization by transmitting a random access preambleon the Physical Random Access Channel (PRACH). The base station providesback some allocated UL resource and timing advance information to allowthe UE to transmit on the PUSCH. Downlink control-plane and user-planedata are scheduled by the Physical Downlink Control Channel (PDCCH) orthe Enhanced Physical Downlink Control Channel (EPDCCH) and the actualdata is transmitted on the Physical Downlink Shared Channel (PDSCH). Thegeneral operations of the physical channels are described in the EUTRAspecifications, for example: “3^(rd) Generation Partnership Project;Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation (TS36.211 Release 8 or later).”

The explosion in data traffic in current cellular networks has motivatedthe need for a rapid expansion of network capacity to cope with thisdemand. In addition, it has been observed that the majority ofdata/video traffic occurs in hotspot and indoor scenarios, wheredata-hungry smartphone applications overwhelm existing networks. As aresult, a major initiative in LTE-Advanced commenced in the LTE Release10 standard with the introduction of a heterogeneous network (HetNet)architecture consisting of small cells, controlled by low power eNodeBnodes, in addition to macro cells controlled by high power eNodeB nodes.These low power nodes are deployed in traffic hot spots andoutdoor/indoor locations to boost capacity and/or improve coverage inareas with spotty macro coverage. Several features have been introducedin LTE Releases 10 and 11 to support efficient HetNet operation with asparse deployment of small cells including enhanced inter-cellinterference coordination (e-ICIC), cooperative multipoint (COMP)transmission/reception and carrier aggregation (CA).

Unfortunately, proposed HetNet solutions fail to take into account adenser deployment of indoor/outdoor small cells with/without macrocoverage. For example, ten or more small cells may be deployed withinthe coverage area of a single macro cell. But proposed HetNet solutionsfail to teach local area enhancements that increase spectral efficiency,and improve overall radio resource management including minimizingsignaling overhead between the Radio Access Network (RAN) and the CoreNetwork. More specifically, what is missing is any teaching for dualconnectivity, wherein a User Equipment (UE) is simultaneously connectedto at least two serving cells controlled by different eNodeBs. Aspectsof this disclosure describe physical layer signaling mechanisms toenable dual connectivity in a wireless cellular system.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a pictorial description of a traditional homogenous networkdeployment of 3 macro cell sites each consisting of three sectors.

FIG. 2 is a description of the relationship between the EUTRAN and theCore Network of a LTE network.

FIG. 3 is a pictorial of a heterogeneous network deployment with severalsmall cells deployed within the coverage area of a macro cell.

FIG. 4 illustrates the mapping of logical, transport and physicalchannels for control/user plane to Master and Secondary eNBs usingdifferent frequencies;

FIG. 5 illustrates the mapping of logical, transport and physicalchannels for control/user plane to Master and Secondary eNBs on the samecarrier frequency;

FIG. 6 illustrates signaling of a reserved set of subframes fortransmission between Master and Secondary eNBs using a bitmap.

FIG. 7 is a block diagram illustrating internal details of a basestation and a mobile user equipment in the network system of FIG. 1suitable for implementing this invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes base stations 101, 102and 103, though in operation, a telecommunications network necessarilyincludes many more base stations. Each of base stations 101, 102 and 103(eNB) are operable over corresponding coverage areas 104, 105 and 106.Each base station's coverage area is further divided into cells. In theillustrated network, each base station's coverage area is divided intothree cells. Handset or other user equipment (UE) 109 is shown in Cell A108. Cell A 108 is within coverage area 104 of base station 101. Basestation 101 transmits to and receives transmissions from UE 109. As UE109 moves out of Cell A 108 and into Cell B 107, UE 109 may be handedover to base station 102. Because UE 109 is synchronized with basestation 101, UE 109 can employ non-synchronized random access toinitiate handover to base station 102.

Non-synchronized UE 109 also employs non-synchronous random access torequest allocation of uplink 111 time or frequency or code resources. IfUE 109 has data ready for transmission, which may be traffic data,measurements report, tracking area update, UE 109 can transmit a randomaccess signal on uplink 111. The random access signal notifies basestation 101 that UE 109 requires uplink resources to transmit the UEsdata. Base station 101 responds by transmitting to UE 109 via downlink(DL) 110, a message containing the parameters of the resources allocatedfor UE 109 uplink transmission along with a possible timing errorcorrection. After receiving the resource allocation and a possibletiming advance message transmitted on downlink (DL) 110 by base station101, UE 109 optionally adjusts its transmit timing and transmits thedata on uplink 111 employing the allotted resources during theprescribed time interval.

Base station 101 configures UE 109 for periodic uplink soundingreference signal (SRS) transmission. Base station 101 estimates uplinkchannel quality information (CSI) from the SRS transmission.

FIG. 2 shows the relation between the EUTRAN of FIG. 1 and the corenetwork 210 in a LTE wireless network. The eNodeBs 203 and 204communicate with the Mobility Management Entity (MME) 211 and theServing Gateway 212 via the S1 signaling interface 205. The UEs 201 and202 communicate over the air interface with eNodeBs 203 and 204respectively. Two eNodeBs are shown in this illustration but there maybe more eNodeBs connected to the same MME in a deployed network. TheeNodeBs communicate with each other over the X2 interface 206.

In LTE Release 11, one approach to base station cooperation in HetNetsis CoMP, wherein a set of transmission points (TPs), for instance,consisting of a macro eNodeB and one or more pico eNodeBs or remoteradio heads, cooperatively transmit or receive data to/from a UE withina geographical area. For the downlink, some specific CoMP schemesinclude joint transmission from a set of transmission points, dynamicpoint selection, dynamic point blanking, and cooperativebeamforming/cooperative scheduling. For the uplink, semi-static pointselection is introduced through the UE-specific configuration of virtualcell IDs for PUSCH/PUCCH transmission. CoMP can operate in both singlecarrier and aggregated carrier scenarios. Coordination between eNodeBsis enabled by signaling over a backhaul communication link. For thepresent LTE specifications the X2 interface specifies the signalingprotocol between eNodeBs.

There are a few inherent limitations of Release 11 HetNet operation whenapplied to a dense small cell deployment. First, a key assumption of theLTE Release 11 CoMP operation is that message exchange betweentransmission points is optimized for ideal backhaul, where ideal meansthat the backhaul is characterized by very low latency (on the order ofa few milliseconds or less) and very high throughput. Therefore,operation in non-ideal backhaul scenarios may reduce the gains shown byCoMP. Second, mobility between cells is more critical in dense networksthan in more traditional homogeneous deployments because additionalcells introduce new cell boundaries with much closer proximity comparedto sparse or homogeneous deployments. For instance, in a dense outdoordeployment, there may be frequent handovers as a UE traverses multiplecell boundaries within a macro cell area. Therefore, it is desirable tominimize the transfer of UE context due to such frequent handoversbetween cells controlled by different eNodeBs and also to minimize theassociated signaling between the RAN and the core network.

One way to address these limitations and improve operational efficiencyin HetNets is to introduce dual connectivity operation between a UE andtwo or more eNodeBs. FIG. 3 shows an exemplary dual connectivityoperation where eNodeB 300 controls a macro cell 310 and a small celllayer is deployed within the coverage of macro cell 301, consisting ofsmall cells 311, 312 and 313 controlled respectively by eNodeBs 301, 302and 303. The eNodeBs 301, 302 and 303 are lower power eNodeBs comparedto 300 and may be pica or femto eNodeBs. The macro cell 310 (orequivalently the eNodeB 300) may provide Control Plane (C-plane)functions over link 330 in the access stratum and non-access stratum andit also provide a mobility anchor for the UE 320 towards the corenetwork. On the other hand, the small cell layer is optimized for theUser Plane (U-plane) and eNodeB 301 offers high throughput and energyefficient transmissions to UE 320 on link 331. These RAN layers mayoperate on separate carriers (F1, F2) or on a shared carrier frequency(co-channel deployment). The eNodeBs involved in dual connectivity areassumed to be connected by a non-ideal backhaul link 333, which ischaracterized by limited capacity and/or significant latency up to tensof milliseconds.

This split of C-plane and U-plane between different network layers orRAN nodes improves handover efficiency by minimizing frequent transfersof UE context between eNodeBs within the coverage area of the eNodeBproviding the mobility anchor to the core network.

A more general definition of dual connectivity is the operation where aUE consumes radio resources provided by at least two different eNodeBsconnected by a latency- and capacity-constrained backhaul link. Theprimary cell is controlled by a Master eNodeB (MeNB) whereas thesecondary cell(s) is controlled by a Secondary eNodeB(s) (SeNB). In thecase of coordination between macro and small cell layers of a HetNet,the MeNB is a macro eNB and the SeNB(s) is a lower power eNB(s)controlling a small cell. However, the methods described in embodimentsof this invention are more general and cover the case where both eNodeBsare in the same power class. Specifically both MeNB and SeNB can bemacro eNodeBs or both can be low power eNodeBs. Embodiments of theinvention disclose physical layer mechanisms that enabledual-connectivity from a UE to two or more eNodeBs, where the eNodeBsmay control cells operating on one or more carrier frequencies.

Mechanisms

Described below are methods for dual connectivity when the cellscontrolled by the MeNB and SeNB are deployed on different carrierfrequencies. At Layer 2 (L2) of the E-UTRA protocol stack, the logical,transport and physical channels of the Medium Access Control (MAC) layermay be partitioned between cells controlled by MeNB and SeNB. Referringnow to FIG. 4 an illustration is shown for an exemplary mapping ofC-plane and U-plane functions to a macro cell controlled by MeNB 400 anda small cell controlled by SeNB 420 respectively. MeNB 400 operates oncarrier frequency F1 and SeNB 420 operates on a different carrierfrequency F2. The multicast channels that support a Multimedia BroadcastMulticast Service (MBMS) 440 can also be assigned a dedicated frequencyF3 or can share the same frequency as either the macro or small cell.This mechanism for inter-node radio resource aggregation bears someslight similarity to carrier aggregation. In carrier aggregation, the UEmaintains a single Radio Resource Control (RRC) connection to thenetwork on a primary serving cell (PCell) and said UE can be configuredfor data transmission/reception in one or more secondary serving cells(SCells) each deployed on a different component carrier. Furthermore,the set of serving cells are controlled by the same eNodeB or an eNodeBconnected to remote radio heads by an ideal backhaul link. In any casethe set of configured serving cells may be considered to be controlledfrom one eNodeB given the ideal backhaul link. In contrast, inter-noderadio resource aggregation, which is characterized by a capacity- andlatency-constrained backhaul link, requires that the UE is aware itconsumes radio resources from at least two eNodeBs. This differencebetween carrier aggregation and dual connectivity introduces a need fornew methods to enable dual connectivity at Layers 1 and 2 of the RANprotocol stack.

The access mechanism for dual connectivity operation is now described.At initial access or when the UE is in the RRC_IDLE state, the UEconnects to a suitable cell based on a set of defined cell selectioncriteria. Dual connectivity may only be configured when the UE is in theRRC_CONNECTED state. The UE performs inter-frequency cell search todiscover suitable small cells, where suitability means a small cell is acandidate for inter-node radio resource aggregation for this UE. Celldiscovery is enabled by detection of the primary and secondarysynchronization signals and received power measurement on thecell-specific reference signals (CRS). As a complementary technique forsmall cell discovery in a dense HetNet a specialized discovery signalcan be used. The UE reports the set of candidate cells to the network.The EUTRAN selects one or more additional cells for the said UE. If aselected target cell is controlled by the same eNodeB, the EUTRAN mayconfigure the UE for carrier aggregation. Otherwise, if the selectedcell is controlled by a different eNodeB, dual connectivity may beconfigured for the UE. For dual connectivity the serving eNB becomes theMeNB whereas the eNB controlling the target cell is configured as theSeNB. The MeNB controls mobility (handover) functions for a UEconfigured for dual connection operation. The UE is configured throughdedicated radio resource control (RRC) signaling for data transmissionto/from a secondary cell, where the cell ID of the secondary cell iscontained in the secondary cell configuration. The UE may be configuredwith a separate Cell Radio Network Temporary Identifier (C-RNTI) for oneor more secondary cells controlled by the SeNB. This C-RNTI is allocatedby a contention-based random access procedure between the UE and theSeNB. Alternatively, if only non-contention based random access ispermitted between the UE and the SeNB, the C-RNTI is provided by RRCsignaling at SeNB addition/configuration. The UE may use the C-RNTIassociated to the SeNB for all uplink transmissions towards the SeNB.This includes generating scrambling sequences and uplink referencesignals based on this C-RNTI.

For dual connectivity the UE is configured to receive PDSCH from boththe MeNB and the SeNB. For the case of a split between control and userplane data, common and dedicated RRC signaling, paging, systeminformation notification and Earthquake and Tsunami Warning service(ETWS) may be transmitted on a primary cell controlled by the MeNB.U-plane data is transmitted on the PDSCH of a secondary cell controlledby a SeNB. In a different embodiment the MeNB may also transmit U-planedata to the UE. This approach is useful for robust or fallback operationbetween macro and small cell layers of a heterogeneous networkdeployment, where the UE moves between two small cells or between asmall cell and macro cell. In a third embodiment both MeNB and SeNBtransmit C-plane and U-plane data to the UE. This method can also beuseful for dual connectivity between nodes of the same power class.

The downlink transmission including Hybrid Automatic Repeat reQuest(HARQ) procedures is now described. For single cell operation or carrieraggregation, HARQ-ACK feedback in response to a data transmission on thePDSCH of one or more serving cells is transmitted on the PUCCH or on thePUSCH if the UE is also scheduled for UL-SCH data transmission. If twoserving eNodeBs are connected by an ideal backhaul link this samemechanism can be followed since the HARQ feedback to a SeNB can berouted through the MeNB within the HARQ-ACK feedback timing budget.However, for a backhaul link with latency greater than the HARQ-ACKfeedback timing budget, the UE should be configured to transmit uplinkcontrol signaling (UCI) on a separate PUCCH for each serving eNodeB.This concept of separate PUCCH is also beneficial for energyconservation at the UE because if the UE is more frequently scheduled ona cell controlled by a nearby eNodeB the required uplink transmit poweris also smaller than that required to transmit to a eNodeB that isfurther away. Therefore, HARQ acknowledgement (HARQ-ACK) feedback inresponse to a PDSCH received from the MeNB in a primary cell istransmitted on PUCCH to the MeNB. Correspondingly, HARQ-ACK feedback inresponse to a PDSCH received from the SeNB in a secondary cell istransmitted on PUCCH to the SeNB. In addition channel state information(CSI) reporting is independently configured for each serving cell. CSIreports for serving cells controlled by the MeNB may be transmitted onPUCCH of a primary cell controlled by the MeNB. CSI reports for servingcells controlled by the SeNB may be transmitted on PUCCH of a secondarycell controlled by the SeNB.

One deployment scenario of dual connectivity can be configuring the UEto transmit or receive data on multiple component carriers for the MeNBand/or the SeNB. This is equivalently a combination of carrieraggregation and dual connectivity. In this case the set of componentcarriers linked to a serving eNodeB are either collocated or connectedby an ideal backhaul link in the case of e.g. remote radio heads. Forthis scenario one serving cell controlled by the MeNB is the primarycell and is the serving cell where the UE transmits on the PUCCH. Oneserving cell controlled by the SeNB is configured for PUCCH transmissionfrom the UE to the SeNB.

To ensure robustness for delay-sensitive applications such as voice,Semi-Persistent Scheduling (SPS) can be configured on a primary cellcontrolled by the MeNB when the MeNB provides the mobility anchor forthe UE towards the core network. In a different embodiment the SeNB mayalso configure a UE for SPS operation.

For independent scheduling of data on radio bearers from MeNB and SeNBrespectively, it may be necessary for the UE to independently requestuplink resources from any of the serving eNodeBs. Therefore, the UE canbe independently configured by either MeNB or SeNB with a PUCCH resourceto transmit a scheduling request (SR). This also minimizes the need forsignaling between MeNB and SeNB for routing requests for uplinkresources. In addition buffer status reports (BSR) can be independentlytransmitted to each serving eNodeB based on which eNodeB configured theassociated radio bearer. As an example, when a buffer status reportneeds to be transmitted to the SeNB and there is no UL-SCH resourceavailable from the SeNB within a defined latency period, the UEtransmits a scheduling request on PUCCH to the SeNB or, if there is novalid PUCCH resource for this purpose, the UE initiates acontention-based random access procedure to the SeNB.

Independent random access procedures may be defined for dualconnectivity. Although LTE Release 11 supports random access procedureon a secondary cell for carrier aggregation, it is limited tocontention-free random access. For dual connectivity with limitedcoordination between eNodeBs the UE should be configured with the fullPRACH configuration of a secondary serving cell controlled by the SeNBfor both contention-free and contention-based random access. For randomaccess on a secondary cell controlled by a SeNB, the entire randomaccess procedure including preamble transmission, random accessresponse, initial uplink transmission corresponding to the random accessresponse grant and contention resolution, if necessary, are performedbetween the UE and SeNB. Therefore, the UE monitors the common searchspace of the secondary cell controlled by the SeNB for random accessresponse messages.

Simultaneous uplink transmission to a MeNB and a SeNB in the sametransmission time interval (TTI) may be limited by the transmit powercapability of a UE. For prior LTE systems a UE may be configured forsimultaneous transmission on PUSCH and PUCCH or on multiple PUSCH whenconfigured for PUSCH transmission on multiple component carriers. Incase the total required power exceeds the UE maximum power capability, apower scaling procedure is followed where PUSCH power is scaled down aslong as UCI is not multiplexed with UL-SCH data on PUSCH. Furthermore,PUCCH power is not scaled down because of the importance of correctlyreceiving the UCI at the eNodeB. For dual connectivity with independentPUCCH and PUSCH to each serving eNodeB, it is important to define how toprioritize power allocation in case the required power exceeds themaximum power capability. Herein we describe some mechanisms for uplinkpower control in case the total required power exceeds the UE maximumpower.

One uplink power control mechanism is to maintain a higher priority forUCI transmission on PUCCH and/or PUSCH compared to UL-SCH data only. Forsimultaneous transmission on PUSCH to one serving eNodeB and PUCCH toanother eNodeB, the PUCCH power is prioritized, wherein the desiredPUCCH power is first allocated and then any residual power may beallocated to PUSCH. For simultaneous transmission of PUCCH to both MeNBand SeNB in the same TTI, the PUCCH power may be equally scaled sinceboth transmissions contain UCI. Other embodiments are possible targetingwhat kind of UCI is actually transmitted. In one such embodiment, ifonly CSI is transmitted on one PUCCH and HARQ-ACK-only or HARQ_ACK+CSIis transmitted on the other PUCCH, the UE may prioritize the PUCCHtransmission containing HARQ-ACK information. These power control rulesmay also be applied to other uplink channels in the event of a transmitpower limitation at a UE. For instance, it may be desired to prioritizepreamble transmission on the PRACH to a serving eNodeB over a PUSCHtransmission only containing UL-SCH data to a different serving eNodeB.

Spectrum remains the most expensive resource in wireless networks. Assuch, it may be desirable to support dual-connectivity for a sharedcarrier HetNet deployment. FIG. 5 shows an exemplary mapping at Layer 2of the RAN protocol stack between logical 510, transport 511 andphysical 512 channels for MeNB 500 and SeNB 520. Here, U-plane data istransmitted on the secondary cell controlled by SeNB 520 whereasC-plane, and possibly U-plane data, may be transmitted in a cellcontrolled by MeNB 500. On the physical layer, the PDSCH and thecorresponding control channels (PDCCH/EPDCCH) are present for both theMeNB and SeNB. Hence, a method to achieve scheduling of datatransmission/reception is required in an orthogonal(interference-coordinated) fashion. Towards this goal the UE shall beconfigured to monitor for downlink control information (DCI) on thePDCCH and/or EPDCCH of cells controlled by both MeNB and SeNB. Differentmultiplexing methods can be configured for this purpose.

In one scheme, time domain multiplexing can be configured for dualconnectivity to the MeNB and SeNB. Herein, a UE is configured with a setof subframes to monitor DCI (PDCCH/EPDCCH) from the MeNB for schedulingC-plane data and possible U-plane data. The UE is configured with adisjoint set of subframes to monitor DCI (PDCCH/EPDCCH) from the SeNBfor scheduling U-plane data.

Multiplexing for DL-SCH data reception may be configured through thechoice of downlink control channel. The UE is configured to monitor thePDCCH or EPDCCH for one serving eNB and another EPDCCH for anotherserving eNB. In an example scenario for a HetNet, the UE is configuredto monitor the PDCCH for the macro cell and the EPDCCH for the smallcell.

Frequency domain multiplexing of control information may be used forscheduling DL-SCH data. In one embodiment for dual connectivity betweenmacro and small cell layers in a HetNet, the UE is configured to monitorthe PDCCH and optionally the EPDCCH on the macro cell. Furthermore, theUE is configured to monitor an independent EPDCCH region(s) using anindependent dedicated ID corresponding to the small cell.

Other multiplexing schemes are possible. In one embodiment involvingsplit of control and user plane between MeNB and SeNB the UE isconfigured to monitor the common search space of the PDCCH for PDSCHtransmission from the MeNB and the UE-specific search space of the PDCCHfor PDSCH transmission from the SeNB.

The same mechanisms to support random access and uplink controlsignaling in the separate frequency scenario can also be applied to theshared carrier case. However, other mechanisms tailored to the sharedcarrier case are also possible.

One such mechanism is HARQ-ACK feedback for FDD. In the case of timemultiplexing of PDSCH transmission from MeNB and SeNB, there is nocollision between HARQ-ACK feedback meant for either serving eNB. Assuch, HARQ-ACK is transmitted on PUCCH to the serving eNB thattransmitted the corresponding PDSCH. For TDD there may be a collisionbetween HARQ-ACK feedback corresponding to PDSCH transmissions from MeNBand SeNB respectively since a single uplink subframe may convey theHARQ-ACK feedback for multiple downlink subframes. In this case, allHARQ-ACK feedback is transmitted to MeNB and the HARQ-ACK feedback meantfor the SeNB is routed over the backhaul. If this routing is notpossible due to unacceptable backhaul latency, the MeNB may coordinatewith the SeNB on which subframes in one or more radio frames it mayschedule PDSCH to a UE operating dual connectivity. The SeNB may notschedule PDSCH in these subframes to said UE in order to avoid collisionof HARQ-ACK feedback from the UE. A bit value ‘1’ indicates that theMeNB may schedule PDSCH in this subframe whereas a bit value ‘0’indicates that the MeNB does not intend to schedule PDSCH to the said UEin this subframe. Referring now to FIG. 6, MeNB 600 coordinatesscheduling opportunities with SeNB 601 using a bitmap 602 of length 10bits corresponding to each radio frame. In this illustration in FIG. 6,the MeNB reserves subframes 0, 4, 5 and 9 for its PDSCH transmission.Other values for the length of the bitmap are not precluded. In oneembodiment the bitmap length is set to a multiple of a radio frames i.e.a multiple of 10 bits. Furthermore, in another embodiment the bitmap canbe set as the least common multiple of the HARQ round trip time and 10bits (for a radio frame).

FIG. 7 is a block diagram illustrating internal details of an eNB 1002and a mobile UE 1001 in the network system of FIG. 1. Mobile UE 1001 mayrepresent any of a variety of devices such as a server, a desktopcomputer, a laptop computer, a cellular phone, a Personal DigitalAssistant (PDA), a smart phone or other electronic devices. In someembodiments, the electronic mobile UE 1001 communicates with eNB 1002based on a LTE or Evolved Universal Terrestrial Radio Access Network(E-UTRAN) protocol. Alternatively, another communication protocol nowknown or later developed can be used.

Mobile UE 1001 comprises a processor 1010 coupled to a memory 1012 and atransceiver 1020. The memory 1012 stores (software) applications 1014for execution by the processor 1010. The applications could comprise anyknown or future application useful for individuals or organizations.These applications could be categorized as operating systems (OS),device drivers, databases, multimedia tools, presentation tools,Internet browsers, emailers, Voice-Over-Internet Protocol (VOIP) tools,file browsers, firewalls, instant messaging, finance tools, games, wordprocessors or other categories. Regardless of the exact nature of theapplications, at least some of the applications may direct the mobile UE1001 to transmit UL signals to eNB (base-station) 1002 periodically orcontinuously via the transceiver 1020. In at least some embodiments, themobile UE 1001 identifies a Quality of Service (QoS) requirement whenrequesting an uplink resource from eNB 1002. In some cases, the QoSrequirement may be implicitly derived by eNB 1002 from the type oftraffic supported by the mobile UE 1001. As an example, VOIP and gamingapplications often involve low-latency uplink (UL) transmissions whileHigh Throughput (HTP)/Hypertext Transmission Protocol (HTTP) traffic caninvolve high-latency uplink transmissions.

Transceiver 1020 includes uplink logic which may be implemented byexecution of instructions that control the operation of the transceiver.Some of these instructions may be stored in memory 1012 and executedwhen needed by processor 1010. As would be understood by one of skill inthe art, the components of the uplink logic may involve the physical(PHY) layer and/or the Media Access Control (MAC) layer of thetransceiver 1020. Transceiver 1020 includes one or more receivers 1022and one or more transmitters 1024.

Processor 1010 may send or receive data to various input/output devices1026. A subscriber identity module (SIM) card stores and retrievesinformation used for making calls via the cellular system. A Bluetoothbaseband unit may be provided for wireless connection to a microphoneand headset for sending and receiving voice data. Processor 1010 maysend information to a display unit for interaction with a user of mobileUE 1001 during a call process. The display may also display picturesreceived from the network, from a local camera, or from other sourcessuch as a Universal Serial Bus (USB) connector. Processor 1010 may alsosend a video stream to the display that is received from various sourcessuch as the cellular network via RF transceiver 1020 or the camera.

During transmission and reception of voice data or other applicationdata, transmitter 1024 may be or become non-synchronized with itsserving eNB. In this case, it sends a random access signal. As part ofthis procedure, it determines a preferred size for the next datatransmission, referred to as a message, by using a power threshold valueprovided by the serving eNB, as described in more detail above. In thisembodiment, the message preferred size determination is embodied byexecuting instructions stored in memory 1012 by processor 1010. In otherembodiments, the message size determination may be embodied by aseparate processor/memory unit, by a hardwired state machine, or byother types of control logic, for example.

eNB 1002 comprises a Processor 1030 coupled to a memory 1032, symbolprocessing circuitry 1038, and a transceiver 1040 via backplane bus1036. The memory stores applications 1034 for execution by processor1030. The applications could comprise any known or future applicationuseful for managing wireless communications. At least some of theapplications 1034 may direct eNB 1002 to manage transmissions to or frommobile UE 1001.

Transceiver 1040 comprises an uplink Resource Manager, which enables eNB1002 to selectively allocate uplink Physical Uplink Shared CHannel(PUSCH) resources to mobile UE 1001. As would be understood by one ofskill in the art, the components of the uplink resource manager mayinvolve the physical (PHY) layer and/or the Media Access Control (MAC)layer of the transceiver 1040. Transceiver 1040 includes at least onereceiver 1042 for receiving transmissions from various UEs within rangeof eNB 1002 and at least one transmitter 1044 for transmitting data andcontrol information to the various UEs within range of eNB 1002.

The uplink resource manager executes instructions that control theoperation of transceiver 1040. Some of these instructions may be locatedin memory 1032 and executed when needed on processor 1030. The resourcemanager controls the transmission resources allocated to each UE 1001served by eNB 1002 and broadcasts control information via the PDCCH.

Symbol processing circuitry 1038 performs demodulation using knowntechniques. Random access signals are demodulated in symbol processingcircuitry 1038.

During transmission and reception of voice data or other applicationdata, receiver 1042 may receive a random access signal from a UE 1001.The random access signal is encoded to request a message size that ispreferred by UE 1001. UE 1001 determines the preferred message size byusing a message threshold provided by eNB 1002. In this embodiment, themessage threshold calculation is embodied by executing instructionsstored in memory 1032 by processor 1030. In other embodiments, thethreshold calculation may be embodied by a separate processor/memoryunit, by a hardwired state machine, or by other types of control logic,for example. Alternatively, in some networks the message threshold is afixed value that may be stored in memory 1032, for example. In responseto receiving the message size request, eNB 1002 schedules an appropriateset of resources and notifies UE 1001 with a resource grant.

Other Embodiments

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription.

Embodiments of this invention apply to various types of frequencydivision multiplex based transmission. Thus, the concept can easily beapplied to: OFDMA, OFDM, DFT-spread OFDM, DFT-spread OFDMA, SC-OFDM,SC-OFDMA, MC-CDMA, and all other FDM-based transmission strategies.

A NodeB is generally a fixed station and may also be called a basetransceiver system (BTS), an access point, or some other terminology. AUE, also commonly referred to as terminal or mobile station, may befixed or mobile and may be a wireless device, a cellular phone, apersonal digital assistant (PDA), a wireless modem card, and so on.

As described in general above, embodiment of the invention may performall tasks described herein such as channel monitoring and precodingselection, formation of transmission signals, etc, using logicimplemented by instructions executed on a processor. Another embodimentmay have particular hardwired circuitry or other special purpose logicoptimized for performing one or more to the tasks described herein.

An embodiment of the invention may include a system with a processorcoupled to a computer readable medium in which a software program isstored that contains instructions that when executed by the processorperform the functions of modules and circuits described herein. Thecomputer readable medium may be memory storage such as dynamic randomaccess memory (DRAM), static RAM (SRAM), read only memory (ROM),Programmable ROM (PROM), erasable PROM (EPROM) or other similar types ofmemory. The computer readable media may also be in the form of magnetic,optical, semiconductor or other types of discs or other portable memorydevices that can be used to distribute the software for downloading to asystem for execution by a processor. The computer readable media mayalso be in the form of magnetic, optical, semiconductor or other typesof disc unit coupled to a system that can store the software fordownloading or for direct execution by a processor.

As used herein, the terms “applied,” “coupled,” “connected,” and“connection” mean electrically connected, including where additionalelements may be in the electrical connection path. “Associated” means acontrolling relationship, such as a memory resource that is controlledby an associated port.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. A method, comprising: configuring a userequipment (UE) for reception of waveforms from more than one basestation (eNB); and communicating using the user equipment (UE) in acellular network utilizing radio resources provided by two distinctschedulers located in two eNBs connected via non-ideal backhaul whereinthe UE communicates with one eNB designated as a master eNB (MeNB) andone eNB designated as a secondary eNB (SeNB), wherein the UE isconfigured to receive a Physical Downlink Shared Channel (PDSCH) fromboth the MeNB and the SeNB; configuring the UE with a first physicaluplink control channel (PUCCH) resource associated with a primaryserving cell (PCell), the PCell being associated with the MeNB;configuring the UE with a second PUCCH resource associated with asecondary serving cell (SCell), the SCell associated with the SeNB;configuring the UE to monitor an enhanced downlink physical controlchannel (EPDCCH) on the PCell during a first set of subframes;configuring the UE to monitor an EPDCCH on the SCell during a second setof subframes, the second set of subframes being different than the firstset of subframes; and transmitting a scheduling request on the PCell orthe SCell using one of the first and second PUCCH resources.
 2. Themethod of claim 1 further comprising the UE designating one of therespective eNBs as a mobility anchor to a core network.
 3. The method ofclaim 1 further comprising the UE designating one of the respective eNBsfor transmission and/or reception of radio resource control (RRC) andnon-access stratum (NAS) signaling.
 4. The method of claim 1 furthercomprising the UE applying procedures for operating a physical uplinkcontrol channel (PUCCH) for both of the respective eNBs.
 5. The methodof claim 1 further comprising the UE applying procedures for receiving aphysical downlink control channel (PDCCH) for both of the respectiveeNBs.
 6. A method of operating a UE, comprising: configuring the userequipment (UE) for reception of waveforms from, or transmission ofwaveforms to, more than one base station (eNB); communicating withserving cells in a master cell group (MCG) and a secondary cell group(SCG) wherein the MCG contains the serving cells of the master eNB(MeNB) and the SCG contains the serving cells of the secondary eNB(SeNB), wherein the UE is configured to receive a Physical DownlinkShared Channel (PDSCH) from both the MeNB and the SeNB; configuring theUE with a first physical uplink control channel (PUCCH) resourceassociated with a primary serving cell (PCell), the PCell beingassociated with the MeNB; configuring the UE with a second PUCCHresource associated with a secondary serving cell (SCell), the SCellassociated with the SeNB; configuring the UE to monitor an enhanceddownlink physical control channel (EPDCCH) on the PCell during a firstset of subframes; configuring the UE to monitor an EPDCCH on the SCellduring a second set of subframes, the second set of subframes beingdifferent than the first set of subframes; and transmitting a schedulingrequest on the PCell or the SCell using one of the first and secondPUCCH resources.
 7. The method of claim 6 further comprising terminatingan S1-U connection for MCG bearers to the serving gateway (S-GW) in theMeNB.
 8. The method of claim 6 further comprising terminating an S1-Uconnection for the split bearers to the serving gateway (S-GW) in theMeNB.
 9. The method of claim 6 further comprising transmitting and/orreceiving radio resource control (RRC) and non-access stratum (NAS)signaling from the MeNB.
 10. The method of claim 6 further comprisingthe UE applying procedures for operating a physical uplink controlchannel (PUCCH) for both the MCG and SCG.
 11. The method of claim 6further comprising the UE applying procedures for receiving a physicaldownlink control channel (PDCCH) for both the MCG and SCG.
 12. A userequipment (UE) apparatus, comprising circuitry configured to: receivewaveforms from, or transmit waveforms to, more than one base station(eNB); and communicate in a cellular network utilizing radio resourcesprovided by two distinct schedulers located in two eNBs connected vianon-ideal backhaul wherein the UE communicates with one eNB designatedas a master eNB (MeNB) and one eNB designated as a secondary eNB (SeNB),wherein the UE is configured to receive a Physical Downlink SharedChannel (PDSCH) from both the MeNB and the SeNB; configure the UE with afirst physical uplink control channel (PUCCH) resource associated with aprimary serving cell (PCell), the PCell being associated with the MeNB;configure the UE with a second PUCCH resource associated with asecondary serving cell (SCell), the SCell associated with the SeNB;configure the UE to monitor an enhanced downlink physical controlchannel (EPDCCH) on the PCell during a first set of subframes; configurethe UE to monitor an EPDCCH on the SCell during a second set ofsubframes, the second set of subframes being different than the firstset of subframes; and transmit a scheduling request on the PCell or theSCell using one of the first and second PUCCH resources.
 13. Theapparatus of claim 12 further comprising the UE designating one of therespective eNBs as a mobility anchor to a core network.
 14. Theapparatus of claim 12 further comprising the UE designating one of therespective eNBs for transmission and/or reception of radio resourcecontrol (RRC) and non-access stratum (NAS) signaling.
 15. The apparatusof claim 12 further comprising the UE applying procedures for operatinga physical uplink control channel (PUCCH) for both of the respectiveeNBs.
 16. The apparatus of claim 12 further comprising the UE applyingprocedures for receiving a physical downlink control channel (PDCCH) forboth of the respective eNBs.
 17. A user equipment (UE) apparatus,comprising circuitry configured to: receive waveforms from, or transmitwaveforms to, more than one base station (eNB); and communicate withserving cells in a master cell group (MCG) and a secondary cell group(SCG) wherein the MCG contains the serving cells of the master eNB(MeNB) and the SCG contains the serving cells of the secondary eNB(SeNB), wherein the UE is configured to receive a Physical DownlinkShared Channel (PDSCH) from both the MeNB and the SeNB; configure the UEwith a first physical uplink control channel (PUCCH) resource associatedwith a primary serving cell (PCell), the PCell being associated with theMeNB; configure the UE with a second PUCCH resource associated with asecondary serving cell (SCell), the SCell associated with the SeNB;configure the UE to monitor an enhanced downlink physical controlchannel (EPDCCH) on the PCell during a first set of subframes; configurethe UE to monitor an EPDCCH on the SCell during a second set ofsubframes, the second set of subframes being different than the firstset of subframes; and transmit a scheduling request on the PCell or theSCell using one of the first and second PUCCH resources.
 18. Theapparatus of claim 17 further comprising terminating an S1-U connectionfor MCG bearers to the serving gateway (S-GW) in the MeNB.
 19. Theapparatus of claim 17 further comprising terminating an S1-U connectionfor the split bearers to the serving gateway (S-GW) in the MeNB.
 20. Theapparatus of claim 17 further comprising transmitting and/or receivingradio resource control (RRC) and non-access stratum (NAS) signaling fromthe MeNB.
 21. The apparatus of claim 17 further comprising the UEapplying procedures for operating a physical uplink control channel(PUCCH) for both the MCG and SCG.
 22. The apparatus of claim 17 furthercomprising the UE applying procedures for receiving a physical downlinkcontrol channel (PDCCH) for both the MCG and SCG.